1. Field of the Invention
The present invention relates to composition of dielectric ceramics, in particular such composition of dielectric ceramics having a sintering property at low temperature, enabling to use, as an internal conductor, Ag or alloys containing a main component of Ag, and a method therefor.
2. Description of the Related Art
Recently, the growth of communication of those moving such as car telephones, pocket telephones and others is remarkable. In the communication of these moving ones, high frequency zone called as quasi microwaves of several 100 MHz to several GHz is used. Therefore, high frequency characteristics are made great account also in electronic devices as resonators, filters or capacitor to be used in the communication instruments of the moving ones. As to the recent popularization of the moving communication, miniaturization and low cost of the communicating instruments are important factors other than improvement of services, and are demanded also in regard to electronic devices.
For example, in materials for resonators, the following characteristics (1) to (4) are required for the using frequency to improve and miniaturize the high frequency characteristics.
(1) Specific dielectric constant is large: The resonator to be used nearly the microwave often utilizes a fact that the wave length is shortened in a dielectric substance in proportion to the inverse number of a square root of dielectric constant, and the length of the resonator can shorten the wave length in proportion of the reverse number of the square root of the dielectric constant.
(2) Q is large: For the materials of the microwave, Q to be defined with Q=1/tan xcex4 is used as valuation of dielectric loss, and that Q is large says the loss is small.
(3) Temperature change of the dielectric constant is small: The temperature change of the resonance frequency of the resonator or the filter is controlled to the utmost, and so it is desirous that the temperature change of the dielectric constant is small.
(4) The sintering at low temperature is possible: For realizing the miniaturization of electronic devices, parts of surface mount devices (SMD) holding conductive electrodes within interiors thereof have been changing to main streams. In this case, it is desirable to use Ag or Cu being low resistance as internal conductive electrodes for heightening the loss characteristics of the electronic device. But Ag or Cu have low melting points, and it is required that compositions for the dielectric ceramics may be sintered at temperature lower than their melting points. The matter of simultaneous sintering is also pointed out when Ag or Cu is made capacitor materials for temperature compensation.
As materials of dielectric ceramics for the microwave, compositions as BaOxe2x80x944TiO2 group or BaO-rare earth oxides-TiO2 group are well known. In particular, as BaOxe2x80x94Nd2O3xe2x80x94TiO2 group is high in the dielectric constant and the Q value, comprehensive studies have been made thereon. Of late years, the sintering at low temperature has been carried out in these compositions, and such technologies are described in patent 2613722 (calcining main components, followed by pulverizing until predetermined powder diameter, and adding sub-components thereto), Japanese patent No. 2781500, Japanese patent No. 2781501, Japanese patent No. 2781502, Japanese patent No. 2781503, and Japanese patent No. 2786977 (these Japanese patents use glass as sub-component), JP-A-5-234420, JP-A-6-211564, JP-A-6-223625, JP-A-7-69719, JP-A-8-55518, JP-A-8-55519, JP-A-8-167322, JP-A-8-167323, JP-A-8-167324, JP-A-8-208328, JP-A-8-208329 (these contain glass as a sub-component), JP-A-3-290359, JP-A-3-295854, JP-A-3-295855, JP-A-3-295856, JP-A-6-116023, JP-A-6-150719, JP-A-6-162822, JP-A-8-55518, JP-A-8-167322, JP-A-8-167323, JP-A-8-167324, JP-A-8-208328, JP-A-8-208329, JP-A-8-245262 (these contain Ge oxide as a sub-component), and other JP-A-61-56407, JP-A-2-44609, JP-A-5-97508, JP-A-6-116023, JP-A-8-157257, and JP-A-8-277161.
In almost all of them, BaO-rare earth oxides-TiO2 are main components to which glass composition or glass composition and several kinds of sub-components are added capable of carrying out the sintering at low temperature. In addition, many of the dielectric materials contain PbO and Bi2O3 in the main components or added components. This is why, since PbO and Bi2O3 also have promoting effects of the sintering at low temperature together with an improving effect of the property such as increasing the dielectric constant, effects of both enable to provide the materials sintered at low temperature for high frequency.
Since the dielectric ceramics of BaOxe2x80x94Nd203xe2x80x94TiO2 group is as mentioned high in the dielectric constant and Q, and small in temperature coefficient of the dielectric constant, it is utilized for dielectric substance for microwave. The sintering at low temperature has recently been realized in BaOxe2x80x94Nd203xe2x80x94TiO2 group, and most of them contain at least one of PbO and Bi203 for improving the properties and promoting the sintering at low temperature.
However, environmental protection campaign of a global scale has lately been raised. Therefore, also in the fields of electronic parts, it is expected to reduce environmental contaminating substances as PbO, Bi2O3 and others. When substances contain environmental contamination, treating facilities of waste liquid or special equipment are necessary in manufacturing processes, and also in view of production cost, it is desirous not to contain such environmental contaminating substances. Further, PbO, and Bi2O3 are easily evaporated at high temperature, and ready for dispersing factors, and yet being neither PbO nor Bi2O3 is desired.
Further, for most of the conventional composition of dielectric ceramics, as mentioned above, the glass composition is indispensable as additives for promoting the sintering, and therefore it is necessary to previously make predetermined glass, inviting cost-up by increasing a production step and enhancing unstable elements. Besides, since a limitation of composition for glass is added due to glazing, an optimum composition is not always realized and properties of dielectric ceramics might be deteriorated. On the other hand, studies have been made on dielectric ceramicss not added with glass, but since many of them necessitate the sintering temperature of 1000xc2x0 C. or higher, there arises a problem that, for example, Ag cannot be used as an internal conductor.
In the conventional composition of dielectric ceramics, in case Ag as the internal conductor is sinterd, it is diffused into an interior of the dielectric substance. Since this Ag diffusion is caused by an Ag concentration gradient, the Ag concentration in the interior of the dielectric substance is not uniform, for example, the Ag concentration is high around the Ag conductor, while it is low in parts separate therefrom. When Ag is diffused in the dielectric substance, the dielectric properties are changed by the Ag concentration, and therefore electronic parts where Ag is the internal conductor will have such dielectric properties made different depending on the parts, causing inconveniences of non-uniform device property so that desired device properties could not be provided. By the Ag diffusion in the dielectric substance, the Ag amount is decreased in the internal conductor, thereby also causing inconveniences of non-uniform device properties so that desired device properties could not be provided.
In case the Ag diffusion amount from the internal conductor into the dielectric substance is much, there is generated a space between the internal conductor and the dielectric substance or caused a leading-in in a portion of the conductor for connecting with an external part, so that an inconvenience as disorder of conduction is caused. In particular, recently miniaturization of high frequency parts has rapidly been advanced, and in response to such conditions, the internal conductor has been made fine pattern or thin in height. Therefore, the above mentioned space between the internal conductor and the dielectric matrix or inconvenience caused by the leading-in in the portion of the conductor for connecting with an external part have been serious problems.
The invention has been realized in view of such circumstances, and it is an object of the present invention to provide a composition of dielectric ceramics which does not contain any environmental contaminating substances such as PbO, Bi2O3 and others, enables to be sintered at low temperature in spite of using no glass composition and which, though employing Ag or Ag alloys as the internal conductor, is least in dispersion of dielectric property due to the Ag diffusion, and enables to provide dielectric ceramics for microwave generating neither occurrence of any space between the internal conductor and the dielectric substance nor any leading-in in the portion of the internal conductor for communicating with the external part, and to offer a method for making such composition of dielectric ceramics.
For accomplishing such an object, the inventive composition of dielectric ceramics is formed in that main components are expressed with a general formula of xBaOxc2x7yNd2O3xc2x7zTiO2 (provided that the general formula has the relation of 6xe2x89xa6xxe2x89xa623, 13xe2x89xa6yxe2x89xa630, 64xe2x89xa6zxe2x89xa668 and x+y+z=100), and in relation with the main components, sub-components are contained of Cu oxides 0.1 to 3.0 wt % in terms of CuO, Zn oxide 0.1 to 4.0 wt % in terms of ZnO, and B oxide 0.1 to 3.0 wt % in term of B2O3.
In the invention, by Cu oxide, Zn oxide and B oxide added in the desired amount together with the main components of BaOxe2x80x94Nd2O3xe2x80x94TiO2 group contained in the desired composition range, while substantially maintaining the dielectric properties, the sintering temperature of the composition of the dielectric ceramics goes down the melting point or lower of Ag or Cu, otherwise alloys of Ag or Cu being a main component.
Further, for accomplishing such an object, the inventive composition of dielectric ceramics is formed in that main components are expressed with a general formula of xBaOxc2x7yNd2O3xc2x7zTiO2 (provided that the general formula has the relation of 6xe2x89xa6xxe2x89xa623, 13xe2x89xa6yxe2x89xa630, 64xe2x89xa6zxe2x89xa668 and x+y+z=100), and in relation with the main components, sub-components are contained of Cu oxides 0.1 to 3.0 wt % in terms of CuO, Zn oxide 0.1 to 4.0 wt % in terms of ZnO, and B oxide 0.1 to 3.0 wt % in term of B2O3, and further preferably contained of Ag 0.3 to 1.5 wt %.
A method for producing the inventive composition of dielectric ceramics comprises the steps of (1) mixing raw materials of BaO, Nd2O3 and TiO2, calcining them at temperature of 1100xc2x0 C. or higher and manufacturing powders of base materials expressed with a general formula of xBaOxc2x7yNd2O3xc2x7zTiO2 (provided that the general formula has the relation of 6xe2x89xa6xxe2x89xa623, 13xe2x89xa6yxe2x89xa630, 64xe2x89xa6zxe2x89xa668 and x+y+z=100); (2) calcining, at temperature of sintering temperature or lower of the base material powders, said powders mixed such that sub-components in relation with the base powders fall into ranges of Cu oxides 0.1 to 3.0 wt % in terms of CuO, Zn oxide 0.1 to 4.0 wt % in terms of ZnO, and B oxide 0.1 to 3.0 wt % in term of B2O3; and (3) pulverizing the calcined powders until predetermined powder diameter.
Further, a method for producing the inventive composition of dielectric ceramics, in the case of containing Ag as a sub-component, comprises the steps of (1) mixing raw materials of BaO, Nd2O3 and TiO2, calcining at temperature of 1100xc2x0 C. or more and making powders of base materials expressed with a general formula of xBaO.yNd2O3.zTiO2 (provided that the main components have the relation of 6xe2x89xa6xxe2x89xa623, 13xe2x89xa6yxe2x89xa630, 64xe2x89xa6zxe2x89xa668 and x+y+z=100); (2) calcining, at temperature of sintering temperature or lower of the base material powders, said powders mixed such that sub-components in relation with the base powders fall into ranges of Cu oxides 0.1 to 3.0 wt % in terms of CuO, Zn oxide 0.1 to 4.0 wt % in terms of ZnO and B oxide 0.1 to 3.0 wt % in term of B2O3, (3) adding to the calcined powders Ag as a further sub-component to be range of 0.3 to 1.5 wt % in relation with the base material powders and pulverizing the calcined powders until predetermined powder diameter. Ag 0.3 to 1.5 wt % may be added in the step (1) or step (2).
In addition, a method for producing the inventive composition of dielectric ceramics employs such an addition form of Ag as the sub-component that is at least one kind of metallic Ag powder, AgNO3, Ag2O and AgCl, and carries out the step (1) at predetermined temperature within the range of 1100 to 1350xc2x0 C.
In the invention, by Cu oxide, Zn oxide and B oxide added in the desired amount together with the main components of BaOxe2x80x94Nd2O3xe2x80x94TiO2 group contained in the desired composition range, while substantially maintaining the dielectric properties, the sintering temperature of the composition of the dielectric ceramics goes down the melting point or lower of Ag or alloys of Ag being a main component, and the Ag added as the sub-component in the desired amount serves to suppress the Ag diffusion into the dielectric substance when Ag or Ag alloys are used as the internal conductor.